This project is directed toward: a) accumulation of heats of hydrogenation of large molecules of biomedical interest, principally unsaturated and polyunsaturated lipids, b) developement and testing of new calorimetric methods for such studies and c) application of the information gained to enthalpemetric analysis of the substances studied. In part: a) hearts of hydrogenation have been determined for acids, methyl esters and triglycerides containing commonly - occurring fatty acid residues with one, two or three double bonds. Present work is directed toward similar studies on less commonly occurring lipids, such as those containing fatty acid residues with four five or six double bonds, mono- and diglycerides and moxed triglycerides. Part b) of the project involves development of new apparatus and methods for use in hydrogen calorimetry carried out in solution. Enthalpimetric analysis of lipids is a very attractive use for the thermochemical information gained in part a) above. Knowing delta Hh, the molar heat of hydrogenation of a pure lipid, and measuring q, the heat of hydrogenation of a sample of unknown purity, one is able to calculate the number of moles, n, in the sample q equals, delta Hh. Present work is an investigation of the use of hydrogen enthalpimetry for mixtures of lipids and for the determination of the degree of unsaturation in small sample e.g. samples in the micromolar region.